The present invention relates to an improved bulkhead design for use in combustors for dual fuel industrial and aeroengine gas turbines.
In a typical state-of-the-art gas turbine for either land based or aero applications, the combustor front end or bulkhead is comprised of several parts including but not limited to (1) a fuel nozzle where air and fuel are mixed together, (2) nozzle guide hardware to accommodate thermal growth and proper tolerancing to enable replacement of a fuel nozzle, (3) bulkhead structure providing mechanical strength and anchoring points for float wall panels and (4) float wall panels which are exposed to the flame and have adequate air cooling to be maintained well below critical material temperatures. In addition, each fuel nozzle must incorporate different levels of sophistication depending on the application. A land based gas turbine fuel nozzle, for example, must provide multiple fuel circuits that support fully premixed mode operation and piloting at part power as well as fuel circuits for gas and liquid fuel types. Managing all of these requirements for a typical engine can be complicated and lead to costly designs in the field or combustor designs that do not get full benefit of potential performance gains achieved by more costly approaches.
The emissions requirements from land based gas turbines are stricter than for aeroengines because the consequence of heavy or bulky control technology are less, i.e. aggressive emission control technologies can be used on ground devices without compromising weight or operability requirements. Moreover, regulation is done by local authorities resulting in a vast array of laws and requirements that an industrial gas turbine must meet. In general, however, industrial engines must produce less than 9 ppm NOx and 9 ppm CO corrected to 15% oxygen without direct water injection into the combustor while operating on natural gas to be competitive in the market place beyond the year 2000. This level of emissions would permit guaranteed emission levels of 15 ppm NOx and 15 ppm CO. Industrial engines must also be capable of running on liquid fuels, i.e. have dual fuel capability, to capture the largest share of the market place. The common practice for surface power gas turbines is to use a lean, premixed combustion strategy. Lean premixed combustion attempts to closely control the combustion temperature and composition, and thereby control NOx formation, UHC and CO oxidation process.
Premixed combustor components must be developed that achieve the required degree of fuel-air premixing without creating zones in the premixer where a flame can stabilize and without promoting a flame structure in the combustor that is prone to acoustic instability coupling, i.e. high levels of pressure fluctuations. The premixing device must be capable of operating over the entire operating range of the engine. This is challenging since the design point for premixing is near to the lean blowout (LBO) limit of the combustor. Therefore, as conditions change from the design point, the operating fuel-air ratio can drop below the associated LBO. Variable geometry air management, piloting schemes or fuel staging of the nozzle is required to maintain the flame fuel-air ratio above LBO while operating at most part power conditions.
Because industrial engines have operating cycles close to aeroengine operating cycles, and because they must operate on liquid fuels in addition to natural gas, they represent a natural technology demonstration platform in the process of developing new technology for aeroengines. In addition, the need for low cost, reliable parts is the same in industrial engines as it is in aeroengines.
The fabrication costs for industrial technology including fuel injector, nozzle guides and bulkhead pieces in some applications are roughly an order of magnitude higher than aeroengines.
Macrolaminate spray atomization technology has been on the market for the past five years from Parker Hannifin Corporation. U.S. Pat. No. 5,435,884 to Simmons et al., and assigned to Parker Hannifin, relates to a method of forming an atomizing spray nozzle which includes the steps of etching a swirl chamber and a spray orifice in a thin sheet of material. The swirl chamber is etched in a first side of the disk and the spray orifice is etched through a second side to the center of the swirl chamber. Feed slots are etched in the first side of the disk extending non-radially to the swirl chamber such that a liquid can be conveyed to the swirl chamber so as to create and sustain the swirling motion. An inlet piece with inlet passage therein is connected with the first side of the disk so as to convey liquid to the feed slots of the disk and to enclose the feed slots and swirl chamber. Macrolaminate atomizers have been shown to produce similar to better atomization relative to comparable traditional designs. This technology has been in production for Westinghouse industrial gas turbine engines. To date, however, this technology has not been applied to bulkhead design.
A similar competing technology has been introduced by Aerojet Incorporated and features platelet technology. Like macrolaminate technology, platelet technology can be used to create intricate passageways in structures that are built by layers of planar etched metals. Both technologies enable fuel-air passageway designs in structures that can efficiently and effectively replace current gas turbine combustor technology.
Accordingly, it is an object of the present invention to provide an improved bulkhead design for use in dual fuel industrial and aeroengine gas turbines.
It is a further object of the present invention to provide a bulkhead design which utilizes macrolaminate, platelet, or similar fabrication technology.
The foregoing objects are attained by the bulkhead design of the present invention.
In accordance with the present invention, a bulkhead for use in dual fuel industrial and aeroengine gas turbines is formed by one or more bulkhead elements. Each bulkhead element includes an air channel and at least one manifold for providing either liquid fuel in droplet form or gas fuel to the air channel to create a fuel-air mixture which is supplied to a combustion chamber. Each bulkhead element, including the air channel and the at least one liquid or gas fuel manifold, is formed by layers of etched material bonded together. Each bulkhead element also may include a cooling air channel for cooling a surface of the bulkhead element on the flame side of the bulkhead. In a preferred embodiment of the present invention, two sets of liquid or gas manifolds supplied by two different liquid or gas fuel plenums are provided in the bulkhead to allow two levels of fuel staging.
Other details of the bulkhead design of the present invention, as well as other objects and advantages attendant thereto, are set forth in the follow detailed description and the accompanying drawings wherein like reference numerals depict like elements.